Conventional semiconductor devices typically comprise a semiconductor substrate, normally made of monocrystalline silicon, and a plurality of dielectric and conductive layers formed thereon. An integrated circuit is formed containing a plurality of conductive patterns comprising conductive lines separated by interwiring spacings, and a plurality of interconnect lines, such as bus lines, bit lines, word lines and logic interconnect lines. Such interconnection lines, made of metal interconnect materials, generally constitute a limiting factor in terms of various functional characteristics of the integrated circuit. As such, there exists a need to provide a reliable interconnection structure capable of achieving higher operating speeds, improved signal-to-noise ration, improved wear characteristics and improved reliability.
Aluminum and aluminum alloys are extensively used as metal interconnect materials. While aluminum-based materials are one of the materials of choice for use as metal interconnects, there are concerns as to whether aluminum can meet the demands required as circuit density and speeds for semiconductor devices increase. Because of these concerns, other materials are under consideration for use as metal interconnect materials in integrated circuits. Copper is one of the materials are under consideration. Advantages associated with the use of copper as a metal interconnect material include a lower susceptibility to electromigration failure (as compared to aluminum) and a lower resistivity (also as compared to aluminum).
One of the problems associated with the use of copper as a metal interconnect material is that copper readily diffuses into surrounding dielectric materials, especially silicon dioxide. In order to inhibit copper diffusion into surrounding dielectric materials, barrier-type materials can be provided to surround copper interconnects. For example, a conductive barrier layer along the side walls and bottom surface of a copper interconnect may be provided. Additionally, a dielectric layer, such as silicon nitride, may be provided on the upper surface of a copper interconnect. This is because silicon nitride is substantially impervious to the diffusion of copper atoms therethrough.
However, there are problems associated with using a silicon nitride layer over a copper interconnect. One problem is that etching procedures for removing silicon nitride from a copper surface tend to corrode or oxidize the copper surface. Corroded copper interconnects lead to short circuits which in turn result in device malfunction or failure. Another problem is that some etching procedures for removing silicon nitride poorly discriminate between silicon nitride and silicon dioxide. This problem results in inadequate trench formation. Yet another problem associated with using a silicon nitride layer over a copper interconnect is that some etching procedures for removing silicon nitride from a copper surface leave relatively large amounts of debris on the copper surface which unnecessarily complicates subsequent cleaning processes.